If they did not replace the connecting rod (I hope I am referring to it correctly), you should take your Z out on the highway, get in the left hand lane at around 60 to 65 mph and see if it changes to the right hand lane on its own in 6 seconds. Make sure you are on a level road, not one with a crown. If it makes the lane change, you need the connecting rod.
My service manager said it was important because if you do have the "drift right" condition, it must be repaired for the alignment (feathering) issue to be correctly resolved. If not, the feathering will return.